Insulin Suppression Test Research Articles

Impact of gender and menopausal status on metabolic parameters in chronic hepatitis C infection.

Hepatitis C infection (HCV) and menopause are associated with insulin resistance (IR), and IR accelerates HCV-induced liver disease. The relationship between menopause and IR has not been studied in this population. This study aimed to assess the impact of menopause on IR and metabolic syndrome in HCV. One hundred and three (69 men, 16 premenopausal, 18 postmenopausal women) noncirrhotic, nondiabetic HCV-infected adults underwent IR measurement via steady-state plasma glucose during a 240-min insulin suppression test. Metabolic syndrome was defined by at least three of five standard laboratory/clinical criteria. The patient characteristics were as follows: mean age 48 years, waist circumference 94.4 ± 12.4 cm and 37.9% Caucasian. SSPG was higher in postmenopausal than premenopausal women or men (mean difference 18, 95% CI -41 to 76 and 35, 95% CI -3 to 72 mg/dL; respectively). After adjusting for waist circumference, female gender, nonwhite race and triglycerides were positively associated and high-density lipoprotein negatively associated with steady-state plasma glucose. Compared to men, both pre- (Coef 48, 95% CI 12-84) and postmenopausal women (Coef 49, 95% CI 17-82) had higher steady-state plasma glucose. Compared to premenopausal women, men (OR 2.0, 95% CI 0.38-10.2) and postmenopausal women (OR 2.9, 95% CI 0.46-18.8) had higher odds of metabolic syndrome, but this was statistically nonsignificant. Both liver inflammation (OR 7.9) and nonwhite race (OR 6.9) were associated with metabolic syndrome. We conclude that women are at inc-reased risk for IR in HCV. There may also be an increased risk of metabolic syndrome postmenopause. Along with lifestyle modification and weight loss, women with metabolic abnormalities represent an especially at-risk group warranting HCV treatment to prevent adverse metabolic outcomes.

Hyperinsulinemia in individuals with obesity: Role of insulin clearance.

ObjectiveSeveral studies have shown decreased insulin clearance rate (ICR) in individuals with obesity, but it remains unclear whether this is predominately due to obesity-associated insulin resistance (IR) or obesity itself. We aimed to clarify the complex interrelationship that exists between obesity, IR and ICR.MethodsHealthy volunteers (n = 277) had measurement of IR and ICR using the insulin suppression test (IST). IR was quantified by determining the steady-state plasma glucose (SSPG) during the IST. ICR was estimated by dividing the insulin infusion rate by the steady-state plasma insulin concentration. We performed our analysis by stratifying the experimental population into 4 dichotomous categories, varying in obesity and IR. Obesity was defined as a body mass index (BMI) ≥ 30 kg/m2, and IR was defined as SSPG ≥ 150 mg/dl.ResultsIndividuals with obesity had higher fasting insulin compared with individuals without obesity, regardless of IR. ICR was similar between individuals with and without obesity but was higher in IR individuals compared with insulin sensitive individuals. In multivariate analysis, both fasting insulin and SSPG were significantly associated with ICR. No significant relationships were observed between BMI and ICR.ConclusionsReduced ICR in obesity is secondary to IR, not excess adiposity.

Effect of Common Genetic Variants of Growth Arrest-Specific 6 Gene on Insulin Resistance, Obesity and Type 2 Diabetes in an Asian Population

ObjectivesGrowth arrest-specific 6 (Gas6), a vitamin K-dependent protein, has been implicated in systemic inflammation, obesity, and insulin resistance (IR). Data from recent studies suggest that polymorphisms in the Gas6 gene are associated with cardiovascular disorders and type 2 diabetes (T2D). However, the association of Gas6 gene variants with obesity, IR, and T2D development has not been explored.Materials and MethodsFour common single nucleotide polymorphisms (SNPs) in the Gas6 gene were genotyped in 984 participants from the Stanford Asia-Pacific Program for Hypertension and Insulin Resistance (SAPPHIRe) family cohort. An insulin suppression test was performed to determine IR based on steady-state plasma glucose (SSPG). Associations between IR indices and obesity, and SNP genotypes, based on previously-reported data for this cohort (Phase I), were analyzed. In the present follow-up study (Phase II), the effects of gene variants of Gas6 on the progression to T2D were explored in individuals who were free of T2D in Phase I. The mean follow-up period for Phase II was 5.7 years.ResultsThe mean age of the study population in Phase I was 49.5 years and 16.7% of individuals developed T2D during follow-up. After adjusting for covariates, three SNPs (rs8191973, rs8197974, and rs7323932) were found to be associated with SSPG levels (p = 0.007, p = 0.03, and p = 0.011, respectively). This association remained significant after multiple testing and showed a significant interaction with physical activity for SNP rs8191973. However, no other significant correlations were observed between Gas6 polymorphisms and other indices of IR or obesity. A specific haplotype, AACG (from rs8191974, rs7323932, rs7331124, and rs8191973), was positively associated with SSPG levels (p = 0.0098). None of the polymorphisms were associated with an increased risk of T2D development.ConclusionsOur results suggest that Gas6 gene variants are associated with IR, although their effects on subsequent progression to T2D were minimal in this prospective Asian cohort.

Salsalate-induced changes in lipid, lipoprotein, and apoprotein concentrations in overweight or obese, insulin-resistant, nondiabetic individuals

Although salsalate administration consistently lowers plasma triglyceride concentrations in patients with type II diabetes, prediabetes, and/or insulin resistance, changes in low-density lipoprotein cholesterol (LDL-C) concentrations have been inconsistent; varying from no change to a significant increase. To evaluate the clinical relevance of this discordance in more detail, we directly measured LDL-C and obtained a comprehensive assessment of changes in lipid, lipoprotein, and apoprotein concentrations associated with salsalate use in insulin-resistant individuals, overweight or obese, but without diabetes, using vertical auto profile method. A single-blind, randomized, placebo-controlled study was performed in volunteers who were overweight or obese, without diabetes, and insulin resistant on the basis of their steady-state plasma glucose concentration during an insulin suppression test. Participants were randomized 2:1 to receive salsalate 3.5 g/d (n = 27) or placebo (n = 14) for 4 weeks. Comprehensive lipid, lipoprotein, and apoprotein analysis by vertical auto profile was obtained after an overnight fast, before and after study intervention. There was no change in directly measured LDL-C concentration in salsalate-treated individuals. However, salsalate administration was associated with various changes considered to decrease atherogenicity; including decreases in triglyceride and total very low-density lipoprotein cholesterol (VLDL-C) concentrations, a shift from small denser LDL lipoproteins toward larger, more buoyant LDL particles, decreases in VLDL(1+2)-C and LDL(4)-C, and nonsignificant decreases in non-high-density lipoprotein cholesterol and apolipoprotein B. No significant changes occurred in the placebo-treated group. Atherogenicity of the lipid, lipoprotein, and apoprotein profile of insulin-resistant individuals who were overweight or obese improved significantly in association with salsalate treatment. The clinical importance of this finding awaits further study.

The receptor CD44 is associated with systemic insulin resistance and proinflammatory macrophages in human adipose tissue.

Proinflammatory immune cell infiltration in human adipose tissue is associated with the development of insulin resistance. We previously identified, via a gene expression-based genome-wide association study, the cell-surface immune cell receptor CD44 as a functionally important gene associated with type 2 diabetes. We then showed that, compared with controls, Cd44 knockout mice were protected from insulin resistance and adipose tissue inflammation during diet-induced obesity. We thus sought to test whether CD44 is associated with adipose tissue inflammation and insulin resistance in humans. Participants included 58 healthy, overweight/moderately obese white adults who met predetermined criteria for insulin resistance or insulin sensitivity based on the modified insulin-suppression test. Serum was collected from 43 participants to measure circulating concentrations of CD44. Subcutaneous adipose tissue was obtained from 17 participants to compare CD44, its ligand osteopontin (OPN, also known as SPP1) and pro-inflammatory gene expression. CD44 expression on adipose tissue macrophage (ATM) surfaces was determined by flow cytometry. Serum CD44 concentrations were significantly increased in insulin-resistant (IR) participants. CD44 gene expression in subcutaneous adipose tissue was threefold higher in the IR subgroup. The expression of OPN, CD68 and IL6 was also significantly elevated in IR individuals. CD44 gene expression correlated significantly with CD68 and IL6 expression. CD44 density on ATMs was associated with proinflammatory M1 polarisation. CD44 and OPN in human adipose tissue are associated with localised inflammation and systemic insulin resistance. This receptor-ligand pair is worthy of further research as a potentially modifiable contributor to human insulin resistance and type 2 diabetes.

Relationship between insulin resistance and amino acids in women and men.

Insulin resistance has been associated with higher plasma amino acid (AA) concentrations, but majority of studies have used indirect measures of insulin resistance. Our main objective was to define the relationship between plasma AA concentrations and a direct measure of insulin resistance in women and men. This was a cross-sectional study of 182 nondiabetic individuals (118 women and 64 men) who had measurement of 24 AAs and steady-state plasma glucose (SSPG) concentration (insulin resistance) using the insulin suppression test. Fourteen out of 24 AA concentrations were significantly (P < 0.05) higher in men than women; only glycine was lower in men. Majority of these AAs were positively associated with SSPG; only glycine concentration was negatively associated. Glutamic acid, isoleucine, leucine, and tyrosine concentrations had the strongest correlation with SSPG (r ≥ 0.4, P < 0.001). The degree of association was similar in women and men, independent of obesity, and similar to traditional markers of insulin resistance (e.g., glucose, triglyceride, high-density lipoprotein cholesterol). Compared with women, men tended to have a more unfavorable AA profile with higher concentration of AAs associated with insulin resistance and less glycine. However, the strength of association between a direct measurement of insulin resistance and AA concentrations were similar between sexes and equivalent to several traditional markers of insulin resistance.

Abnormalities of lipoprotein concentrations in obstructive sleep apnea are related to insulin resistance.

Prevalence of cardiovascular disease (CVD) is increased in patients with obstructive sleep apnea (OSA), possibly related to dyslipidemia in these individuals. Insulin resistance is also common in OSA, but its contribution to dyslipidemia of OSA is unclear. The study's aim was to define the relationships among abnormalities of lipoprotein metabolism, clinical measures of OSA, and insulin resistance. Cross-sectional study. OSA severity was defined by the apnea-hypopnea index (AHI) during polysomnography. Hypoxia measures were expressed as minimum and mean oxygen saturation, and the oxygen desaturation index. Insulin resistance was quantified by determining steady-state plasma glucose (SSPG) concentrations during the insulin suppression test. Fasting plasma lipid/lipoprotein evaluation was performed by vertical auto profile methodology. Academic medical center. 107 nondiabetic, overweight/obese adults. Lipoprotein particles did not correlate with AHI or any hypoxia measures, nor were there differences noted by categories of OSA severity. By contrast, even after adjustment for age, sex, and BMI, SSPG was positively correlated with triglycerides (r = 0.30, P < 0.01), very low density lipoprotein (VLDL) and its subclasses (VLDL1+2) (r = 0.21-0.23, P < 0.05), and low density lipoprotein subclass 4 (LDL4) (r = 0.30, P < 0.01). SSPG was negatively correlated with high density lipoprotein (HDL) (r = -0.38, P < 0.001) and its subclasses (HDL2 and HDL3) (r = -0.32, -0.43, P < 0.01), and apolipoprotein A1 (r = -0.33, P < 0.01). Linear trends of these lipoprotein concentrations across SSPG tertiles were also significant. Pro-atherogenic lipoprotein abnormalities in obstructive sleep apnea (OSA) are related to insulin resistance, but not to OSA severity or degree of hypoxia. Insulin resistance may represent the link between OSA-related dyslipidemia and increased cardiovascular disease risk.

Usefulness of Fetuin-A to Predict Risk for Cardiovascular Disease Among Patients With Obstructive Sleep Apnea

Patients with obstructive sleep apnea (OSA) are at increased risk for cardiovascular diseases (CVDs). Fetuin-A, a novel hepatokine, has been associated with the metabolic syndrome (MetS), insulin resistance, and type 2 diabetes mellitus, all of which are highly prevalent in patients with OSA and associated with increased CVD risk. The goal of this study was to determine whether fetuin-A could be involved in the pathogenesis of CVD risk in patients with OSA, through relations of fetuin-A with MetS components and/or insulin resistance. Overweight or obese, nondiabetic volunteers (n = 120) were diagnosed with OSA by in-laboratory nocturnal polysomnography. Steady-state plasma glucose concentrations derived during the insulin suppression test were used to quantify insulin-mediated glucose uptake; higher steady-state plasma glucose concentrations indicated greater insulin resistance. Fasting plasma fetuin-A and lipoprotein concentrations were measured. Whereas neither the prevalence of MetS nor the number of MetS components was associated with tertiles of fetuin-A concentrations, the lipoprotein components of MetS, triglycerides and high-density lipoprotein cholesterol, increased (p <0.01) and decreased (p <0.05), respectively, across fetuin-A tertiles. Additionally, comprehensive lipoprotein analysis revealed that very low density lipoprotein (VLDL) particles and VLDL subfractions (VLDL1+2 and VLDL3) were increased across fetuin-A tertiles. In contrast, neither insulin resistance nor sleep measurements related to OSA were found to be modified by fetuin-A concentrations. In conclusion, abnormalities of lipoprotein metabolism, but not MetS or insulin resistance per se, may represent a mechanism by which fetuin-A contributes to increased CVD risk in patients with OSA.

Clinical Biopotency of Insulin Analogues: Comparative Assessment in Different Species

ObjectiveThe clinical potency of human insulin has classically been evaluated following the U.S. Pharmacopeia (USP) guideline for comparison to an international standard (IS) of activity (IU). However, since insulin analogues cannot be standardized against IS, there is a need for a bioassay to assess clinical specific activity (U). To this extent, we compared the biopotency (U) of different insulin products in different species and used human (recombinant) and pork (natural) insulin as reference standards.Methods: New Zealand White rabbits were fasted and injected subcutaneously (s.c.) at a dose level of 0.5 U/kg. Diabetic Yucatan miniature swine (Sus scrofa) were injected s.c. at dose level of 0.1 U/kg. Normal insulin suppression tests (nIST) were conducted in primates (Macaca fascicularis) receiving a bolus intravenous (i.v.) infusion of glucose. Insulin products were given at dose level of 0.05 U/kg. Glucose levels were recorded using handheld glucometer devices. The blood glucose kinetic (BGPK), the blood glucose area under the curve (BGAUC) and the slope of the blood glucose clearance rate (kG) were used to assess clinical biopotency.Results: The BGPK for short‐acting human and pork insulin were similar in the rabbit assay but their respective BGAUCs were different (ratio of 1.2). Accordingly pork insulin was more potent during nIST in the non‐human primate (slope of ‐0.012 vs. ‐0.010; pork and human, respectively).ConclusionOur data indicate that the clinical biopotency of insulin products can be assessed using BGAUC and kG, but that only the type 1 diabetic miniature swine can discriminate between differences in clinical biopotency for all aspects of BGPK.

Identification and validation of N-acetyltransferase 2 as an insulin sensitivity gene.

Decreased insulin sensitivity, also referred to as insulin resistance (IR), is a fundamental abnormality in patients with type 2 diabetes and a risk factor for cardiovascular disease. While IR predisposition is heritable, the genetic basis remains largely unknown. The GENEticS of Insulin Sensitivity consortium conducted a genome-wide association study (GWAS) for direct measures of insulin sensitivity, such as euglycemic clamp or insulin suppression test, in 2,764 European individuals, with replication in an additional 2,860 individuals. The presence of a nonsynonymous variant of N-acetyltransferase 2 (NAT2) [rs1208 (803A>G, K268R)] was strongly associated with decreased insulin sensitivity that was independent of BMI. The rs1208 "A" allele was nominally associated with IR-related traits, including increased fasting glucose, hemoglobin A1C, total and LDL cholesterol, triglycerides, and coronary artery disease. NAT2 acetylates arylamine and hydrazine drugs and carcinogens, but predicted acetylator NAT2 phenotypes were not associated with insulin sensitivity. In a murine adipocyte cell line, silencing of NAT2 ortholog Nat1 decreased insulin-mediated glucose uptake, increased basal and isoproterenol-stimulated lipolysis, and decreased adipocyte differentiation, while Nat1 overexpression produced opposite effects. Nat1-deficient mice had elevations in fasting blood glucose, insulin, and triglycerides and decreased insulin sensitivity, as measured by glucose and insulin tolerance tests, with intermediate effects in Nat1 heterozygote mice. Our results support a role for NAT2 in insulin sensitivity.

In vivo 2H2O administration reveals impaired triglyceride storage in adipose tissue of insulin-resistant humans

Indirect evidence suggests that impaired triglyceride storage in the subcutaneous fat depot contributes to the development of insulin resistance via lipotoxicity. We directly tested this hypothesis by measuring, in vivo, TG synthesis, de novo lipogenesis (DNL), adipocyte proliferation, and insulin suppression of lipolysis in subcutaneous adipose tissue of BMI-matched individuals classified as insulin resistant (IR) or insulin sensitive (IS). Nondiabetic, moderately obese subjects with BMI 25-35 kg/m(2), classified as IR or IS by the modified insulin suppression test, consumed deuterated water ((2)H2O) for 4 weeks. Deuterium incorporation into glycerol, palmitate, and DNA indicated TG synthesis, DNL, and adipocyte proliferation, respectively. Net TG synthesis and DNL in adipose cells were significantly lower in IR as compared with IS subjects, whereas adipocyte proliferation did not differ significantly. Plasma FFAs measured during an insulin suppression test were 2.5-fold higher in IR subjects, indicating resistance to insulin suppression of lipolysis. Adipose TG synthesis correlated directly with DNL but not with proliferation. These results provide direct in vivo evidence for impaired TG storage in subcutaneous adipose tissue of IR as compared with IS. Relative inability to store TG in the subcutaneous depot may represent a mechanism contributing to the development of insulin resistance in the setting of obesity.

Effect of Growth Hormone on Dawn Phenomenon in Healthy Adults

The purpose of this study was to investigate the involvement of growth hormone in the diurnal variation of insulin sensitivity in healthy adults. Afternoon (16:00 hr) or night (23:00 hr) pretreatment with a subcutaneous injection of normal saline, human growth hormone to mimic the normal nocturnal rise in growth hormone, or octreotide to inhibit endogenous growth hormone secretion to create a state of relative nocturnal growth hormone deficiency, was given 16 hours before undergoing the modified insulin suppression test in healthy subjects. The morning and evening experiments were separated by an interval of at least 3 days. Thus, each subject was tested on six separate occasions arranged in a random order. A higher value of the steady-state plasma glucose (SSPG) is indicative of lower insulin sensitivity. Plasma glucose, serum insulin, insulin-like growth factor-1, nonesterified fatty acids (NEFA), and metabolic clearance rate of insulin (MCRI) were measured. In the normal saline and human growth hormone groups, SSPG levels were lower in the morning than in the evening. Evening SSPG levels, MCRI, and NEFA concentrations were higher in the participants treated with normal saline and growth hormone than in the octreotide group. Differences in SSPG levels between the morning and evening values were higher in the participants pretreated with normal saline and growth hormone than in those treated with octreotide. A diurnal variation in insulin sensitivity existed in healthy subjects. These results provided direct evidence that the role of growth hormone in regulating insulin sensitivity might be related to changes in the MCRI and the metabolism of NEFA in healthy subjects.

Modulation of coronary heart disease risk by insulin resistance in subjects with normal glucose tolerance or prediabetes.

This study was based on the hypothesis that: (1) coronary heart disease (CHD) risk is accentuated in the insulin-resistant subset of persons with normal glucose tolerance (NGT) or prediabetes (PreDM); (2) the prevalence of insulin resistance, and associated abnormalities, is greater in subjects with PreDM; and (3) insulin resistance is the major contributor to increased CHD risk in these individuals. A 75 g oral glucose challenge was used to classify volunteers as having NGT or PreDM. Steady-state plasma glucose (SSPG) concentrations during the insulin suppression test subdivided both groups into insulin sensitive (IS = SSPG < 8.4 mmol/L) or resistant (IR = SSPG ≥ 8.4 mmol/L). Measurements were made of demographic characteristics, blood pressure, and lipid and lipoprotein concentrations, and comparisons made between the subgroups. Subjects with PreDM (n = 127) were somewhat older, more likely to be non-Hispanic men, with increased adiposity than those with NGT (n = 315). In addition, they had higher FPG concentrations, were insulin resistant (SSPG concentration; 11.4 vs. 7.2 mmol/L), with higher blood pressures, and a significantly more adverse CHD risk lipid profile (p < 0.001). Twice as many subjects with PreDM were IR (72 vs. 35 %), and the CHD risk profile was significantly worse in the IR subgroups in those with either NGT or PreDM. Coronary heart disease risk profile is significantly more adverse in subjects with PreDM as compared to individuals with NGT. However, glucose tolerance status is not the only determinant of CHD risk in nondiabetic individuals, and differences in degree of insulin resistance significantly modulate CHD risk in subjects with NGT or PreDM.

Association between insulin resistance and cognition in patients with depressive disorders: Exploratory analyses into age-specific effects

The current preliminary cross sectional study sought to examine the effects of insulin resistance (IR) and body mass index (BMI) on cognitive performance in adult patients with a history depression, currently not in an acute Major Depressive Episode (MDD). As an exploratory post hoc investigation, special consideration was given to adults <45 years and ≥45 years old.Subjects included men and women ages 19-71 (N = 39) with a history of a non-psychotic, non-melancholic MDD. All subjects underwent an insulin suppression test to determine Steady-State Plasma Glucose (SSPG), a battery of neuropsychological tests, and measurement of BMI. Multiple linear regressions were conducted to determine whether there were differential effects of direct (SSPG) and indirect (BMI) measures on cognition in the whole sample and within dichotomized age groups (<45 and ≥45 years).Preliminary results showed that in the sample as a whole, SSPG was not associated with worse performance on any cognitive variables, while higher BMI was associated with worse dominant hand fine motor skills. Within age groups, differential effects on cognition were found in relation to SSPG and BMI. Higher SSPG was associated with worse cognitive flexibility in the group <45 years, whereas higher BMI was associated with worse estimate of global intelligence in the group ≥45 years.The potential negative impact of IR in younger adults with depression raises concerns regarding the long-term impact on cognition and risk for Alzheimer's disease in undiagnosed younger adults with IR and depression. These negative consequences may not be seen with indirect measures of IR in younger adult populations. Overweight and obesity in older adults with a history of depression appear to have further negative impacts on cognition similar to deficits seen in patients with diabetes. ClinicalTrials.gov IdentifierClinical Trial NCT01106313

Depression is not associated with peripheral insulin resistance in patients with chronic hepatitis C infection.

Depression is common in individuals infected with hepatitis C virus (HCV), and both depression and HCV infection are independently associated with insulin resistance (IR). To evaluate the relationship between depression and IR, among other factors, in an HCV-infected cohort. In this cross-sectional analysis, seventy-four non-type 2 diabetic, noncirrhotic, HCV-infected patients underwent comprehensive clinical, histologic and metabolic evaluation. IR was assessed directly with an insulin suppression test by measuring steady-state plasma glucose (SSPG) levels during continuous infusions of octreotide, glucose and insulin. Logistic regression modelling was used to evaluate predictors associated with depression. Thirty-nine (53%) patients were depressed, and 21 (54%) depressed patients were on at least one antidepressant. A higher estimated proportion of depressed patients were Caucasian (51% vs 20%, P = 0.005), unemployed (69% vs 49%, P = 0.07), heavier smokers (18 pack-years vs 13 pack-years, P = 0.07), on substance abuse therapy (16% vs 3%, P = 0.06) and had lower HDL levels (1.2 mmol/L vs 1.4 mmol/L, P = 0.01). The mean SSPG levels in depressed and nondepressed patients were 7.3 and 8.3 mmol/L (P = 0.45), respectively. In multipredictor adjusted analysis, only Caucasian race (OR 4.19, 95% CI 1.42-12.35, P = 0.009) and lower HDL (OR 0.95, 95% CI 0.89-0.99, P = 0.046) were associated with depression. In conclusion, although prevalent, depression was not associated with peripheral IR in this HCV-infected cohort. Attention to other modifiable factors associated with depression in the HCV-infected population is warranted.

Relationship among 25-hydroxyvitamin D concentrations, insulin action, and cardiovascular disease risk in patients with essential hypertension.

Although low plasma 25-hydroxyvitamin D (25(OH)D) concentrations have been shown to predict risk of hypertension and associated cardiovascular disease (CVD), vitamin D repletion has not consistently lowered blood pressure or decreased CVD. One possibility for this discrepancy is the presence of considerable metabolic heterogeneity in patients with hypertension. To evaluate this possibility, we quantified relationships among insulin resistance, 25(OH)D concentration, and CVD risk factor profile in patients with essential hypertension. Measurements were made of 25(OH)D concentrations, multiple CVD risk factors, and insulin resistance by the steady-state plasma glucose concentration during the insulin suppression test in 140 otherwise healthy patients with essential hypertension. As a group, the patients were overweight/obese and insulin resistant and had low 25(OH)D concentrations. The more insulin resistant the patients were, the worse the CVD risk profile was. In addition, the most insulin-resistant quartile had significantly lower 25(OH)D concentrations than the most insulin-sensitive quartile (20.3±1.4 vs. 25.8±1.4ng/ml; P = 0.005). In the entire group, 25(OH)D concentration significantly correlated with magnitude of insulin resistance (steady-state plasma glucose concentration; r = -0.20; P = 0.02). There was considerable metabolic heterogeneity and substantial difference in magnitude of conventional CVD risk factors in patients with similar degrees of blood pressure elevation. The most insulin-resistant quartile of subjects had the lowest 25(OH)D concentration and the most adverse CVD risk profile, and they may be the subset of patients with essential hypertension most likely to benefit from vitamin D repletion.

Effect of salsalate on insulin action, secretion, and clearance in nondiabetic, insulin-resistant individuals: a randomized, placebo-controlled study.

OBJECTIVESalsalate treatment has been shown to improve glucose homeostasis, but the mechanism remains unclear. The aim of this study was to evaluate the effect of salsalate treatment on insulin action, secretion, and clearance rate in nondiabetic individuals with insulin resistance.RESEARCH DESIGN AND METHODSThis was a randomized (2:1), single-blind, placebo-controlled study of salsalate (3.5 g daily for 4 weeks) in nondiabetic individuals with insulin resistance. All individuals had measurement of glucose tolerance (75-g oral glucose tolerance test), steady-state plasma glucose (SSPG; insulin suppression test), and insulin secretion and clearance rate (graded-glucose infusion test) before and after treatment.RESULTSForty-one individuals were randomized to salsalate (n = 27) and placebo (n = 14). One individual from each group discontinued the study. Salsalate improved fasting (% mean change −7% [95% CI −10 to −14] vs. 1% [−3 to 5], P = 0.005) but not postprandial glucose concentration compared with placebo. Salsalate also lowered fasting triglyceride concentration (−25% [−34 to −15] vs. −6% [−26 to 14], P = 0.04). Salsalate had no effect on SSPG concentration or insulin secretion rate but significantly decreased insulin clearance rate compared with placebo (−23% [−30 to −16] vs. 3% [−10 to 15], P < 0.001). Salsalate was well tolerated, but four individuals needed a dose reduction due to symptoms.CONCLUSIONSSalsalate treatment in nondiabetic, insulin-resistant individuals improved fasting, but not postprandial, glucose and triglyceride concentration. These improvements were associated with a decrease in insulin clearance rate without change in insulin action or insulin secretion.

Gerald M. Reaven, MD: Demonstration of the central role of insulin resistance in type 2 diabetes and cardiovascular disease.

Gerald M. Reaven, MD, could easily be epitomized as the “Father of Insulin Resistance.” (For those who do not know Dr. Reaven, he would humbly raise objection to being called Dr. Reaven rather than Jerry.) That said, Jerry is credited with developing the insulin suppression test, the first quantitative method to measure insulin-mediated glucose uptake in humans (1). Using this technique, he established the importance of insulin resistance in human disease, and importantly, in type 2 diabetes (2,3). In nondiabetic individuals, he demonstrated the role of insulin resistance/compensatory hyperinsulinemia in the development of 1 ) hypertriglyceridemia (4) and low HDL concentrations (5), 2 ) decreased urinary uric acid clearance and hyperuricemia (6), 3 ) decreased LDL particle diameter (7), 4 ) enhanced postprandial lipemia and remnant lipoprotein accumulation (8), 5 ) increased levels of plasminogen activator inhibitor-1 (9), 6 ) salt sensitivity (10), 7 ) essential hypertension (11), and 8 ) increased sympathetic nervous system activity (12). In addition to emphasizing the role of insulin resistance/compensatory hyperinsulinemia in increasing the likelihood of an individual developing one or more of the consequences listed above, he first pointed out the clustering of these abnormalities. It is clear now that this group of clinical abnormalities, initially designated Syndrome X, is an important factor leading to cardiovascular disease. Syndrome X was introduced to the medical community in his now famous Banting Lecture in 1988 (13) and only later became known as metabolic syndrome. Jerry was born in Gary, IN, on 28 July 1928, but spent most of his precollege years living in Cleveland, OH, thus accounting for his lifelong allegiance to the Cleveland Indians baseball team and a great deal of frustration on his part during their many less-than-stellar seasons. Jerry matriculated at the University of Chicago and graduated in 1949, also the year of his marriage to his …

Identification of Insulin Resistance in Subjects with Normal Glucose Tolerance

Decreased insulin action (insulin resistance) is crucial in the pathogenesis of type 2 diabetes. Decreased insulin action can even be found in normoglycaemic patients, and they still bear increased risks for cardiovascular disease. In this study, we built models using data from metabolic syndrome (Mets) components and the oral glucose tolerance test (OGTT) to detect insulin resistance in subjects with normal glucose tolerance (NGT). In total, 292 participants with NGT were enrolled. Both an insulin suppression test (IST) and a 75-g OGTT were administered. The steady-state plasma glucose (SSPG) level derived from the IST was the measurement of insulin action. Participants in the highest tertile were defined as insulin-resistant. Five models were built: (i) Model 0: body mass index (BMI); (ii) Model 1: BMI, systolic and diastolic blood pressure, triglyceride; (iii) Model 2: Model 1 + fasting plasma insulin (FPI); (iv) Model 3: Model 2 + plasma glucose level at 120 minutes of the OGTT; and (v) Model 4: Model 3 + plasma insulin level at 120 min of the OGTT. The area under the receiver operating characteristic curve (aROC curve) was observed to determine the predictive power of these models. BMI demonstrated the greatest aROC curve (71.6%) of Mets components. The aROC curves of Models 2, 3, and 4 were all substantially greater than that of BMI (77.1%, 80.1%, and 85.1%, respectively). A prediction equation using Mets components and FPI can be used to predict insulin resistance in a Chinese population with NGT. Further research is required to test the utility of the equation in other populations and its prediction of cardiovascular disease or diabetes mellitus.

Does Polycystic Ovarian Syndrome Increase Insulin Resistance Above and Beyond Obesity?

Objective: Although obesity and insulin resistance are common in women with polycystic ovarian syndrome (PCOS), PCOS is generally believed to independently raise the risk of insulin resistance. However, only a few studies have used direct measures of insulin resistance, and they have included few subjects. The objective of this study was to compare the relationship between body mass index (BMI) and insulin resistance in a relatively large sample size of women, with and without PCOS, using a specific measure of insulin action. Methods: We compared 94 women with PCOS based on the 1990 NIH criteria with 72 controls with eumenorrhea less than 40 years old. Degree of insulin resistance was quantified using the insulin suppression test. Fasting glucose and lipid concentrations and blood pressure were also measured. Results: There was a significant and comparable relationship between BMI and insulin resistance in women with and without PCOS (r=0.55, p<0.001 in PCOS, r=0.53, p<0.001 in Control). In a linear model adjusted for age and BMI, PCOS was not significantly associated with insulin resistance. PCOS was significantly associated with systolic blood pressure (p=0.03) but not triglyceride, high-density lipoprotein cholesterol and fasting glucose concentration. Conclusion: Challenging previous studies, we find that PCOS is not independently associated with insulin resistance beyond obesity. PCOS, however, may independently increase systolic blood pressure.